This invention relates to a throttle sensor for sensing opening degree of a throttle valve of an engine and outputting an electric signal corresponding to the opening degree.
Conventionally, two methods are available for opening and closing a throttle valve of an engine. One of the methods is a mechanical method wherein the throttle valve is opened and closed by transmitting depression operation of an acceleration pedal to a throttle cable and rotating a throttle lever through the throttle cable. The other is an electrical method wherein the throttle valve is opened and closed by converting an amount of depression of the acceleration pedal to an electrical signal and opening and closing the throttle valve by a motor actuatable in response to the electrical signal as converted. In both the above-mentioned methods, a throttle shaft mounting the throttle valve is connected to a variable resistor so that the throttle shaft may be interlocked with the opening and closing operations of the throttle valve, and a throttle sensor is used for outputting an electrical signal corresponding to the opening and closing operations of the throttle valve and for sensing opening degree of the throttle valve.
As shown in FIG. 1, a conventional throttle sensor 1 includes resistors 2, 3, 4 and 5, a slide member or wiper 6 slidably contacting with the resistors 2 and 3, a slide member or wiper 7 slidably contacting with the resistors 4 and 5, and a slide portion 8 mounting both the slide members 6 and 7. The slide portion 8 is so arranged as to be interlocked with rotation of a throttle shaft 14 mounting a throttle valve 13 as shown in FIG. 4, and the slide member 6 serves to change resistance between both the resistors 2 and 3 in dependence upon opening and closing operations of the throttle valve 13, while the slide member 7 serving to change resistance between both the resistors 4 and 5. In the case that +5 V of DC 5 V constant voltage power supply is applied to a terminal Vc of the resistor 5, and 0 V of the DC 5 V constant voltage power supply is applied to a terminal E of the resistor 2, a voltage outputted from a terminal VTA of the resistor 3 is linearly changed in proportion to rotation of the slide portion 8, and as the throttle valve 13 is driven in its closing direction, the voltage outputted from the terminal VTA of the resistor 3 is reduced. Further, the resistor 4 has a cut portion 9, and under almost closed condition of the throttle valve 13, that is under idling condition, a voltage outputted from a terminal IDL of the resistor 4 becomes +5 V.
Accordingly, a set of variable resistors composed of the resistors 2 and 3 and the slide member 6 serves as a throttle sensor L for outputting an electrical signal corresponding to opening degree of the throttle valve 13 from the terminal VTA, while another set of variable resistors composed of the resistors 4 and 5 and the slide member 7 serves as an idling switch I for outputting an electrical signal of +5 V from the terminal IDL under idling condition and outputting an electrical signal of 0 V when the throttle valve is driven in its opening direction. FIG. 2 shows an electrical circuit diagram of the throttle sensor 1 having the above-mentioned function, and FIG. 3 shows a characteristic graph of FIG. 2.
As shown if FIG. 4, the throttle sensor 1 is fixed at its elongated hole 10 to a throttle body 11 at its screw hole 12 by a screw and the like. A throttle shaft 14 mounting a throttle valve 13 is connected to the slide portion 8 of the throttle sensor 1, and when position of the slide portion 8 of the throttle sensor 1 relative to opening degree of the throttle valve 13 is determined, slight adjustment of positioning of the slide portion 8 is permitted with the aid of the elongated hole 10 of the throttle sensor 1. Such a relative position of the slide portion 8 to the opening degree of the throttle valve 13 is important for determining an amount of fuel to be injected by command of a computer 15 to which an electrical signal outputted from the terminal VTA of the throttle sensor 1 is inputted, and also for determining whether the engine is under idling control or acceleration and deceleration control when an electrical signal outputted from the terminal IDL of the idle switch I is inputted to the computer 15. In the event that the position of the throttle valve 13, that is, the position of the slide portion 8 under almost closed condition of the throttle valve 13 or idling condition, is not accurately set, the voltage to be outputted from the terminal IDL will become 0 V, but not +5 V, and as a result, the acceleration and deceleration control for fuel injection control is decided by the computer 15, thereby deteriorating driving feeling of a vehicle.
Further, when the throttle sensor 1 and the throttle body 11 are initially set, respective voltages to be outputted from the terminals VTA and IDL of the throttle sensor 1 are measured by using a digital voltmeter and the like with an accuracy of a milivolt unit. To this end, relative position of the throttle sensor 1 to the throttle body 11 must be mechanically adjusted in the range of the elongated hole 10 of the throttle sensor 1, which requires a large number of awkward acts. Further, in the event that the screws fixed to the throttle sensor 1 and the throttle body 11 are loosened because of vibrations during the vehicle operation after initial setting to create deviation of the relative position of the slide portion 8 of the throttle sensor 1 with respect to the opening degree of the throttle valve 13 owing to a free space of the elongated hole 10, the relative position of the throttle sensor 1 to the throttle body 11 must by adjusted again in the same way as the initial setting, which is also awkward requiring a large number of steps.